In the manufacture of colored sealants, it has become desirable to mix coloring agents with the sealant as close as possible to the area of packaging of the material. This is referred to as "point of packaging" pigmentation. The general idea is to mix pigment into the base sealant at the last possible moment before filling a package, such as a cartridge, tube, drum, or other container. In these types of processes, a clean-up would be limited to the pigment mixing process at the end of the production line.
Currently, processes for coloring sealants involve frequent changeovers from color to color. First, the base sealant is compounded using known technology, catalyzed, and packaged in drums or bulk containers. The containers are moved to a separate color production process area for pigmentation. Many different color pigments are needed in order to make the variety of colors and shades required by the market place. Matching a specific desired color can require sophisticated blending of a number of pigments. Typically, production personnel load the base sealant into a large mixer, and meter the necessary coloring agent into the mixer to produce a desired colored sealant. The ingredients are mixed for a given time and checked for a good color match using standard colorimetry technology. The addition of pigment must be limited because the pigment can cause degradation of the physical properties of the sealant if it exceeds a certain concentration.
When the color of the sealant is determined to be correct, the sealant is moved to a proportionating machine where the sealant is dosed into cartridges, drums, or pails through the use of a one-part volumetric dosing system. When the packaging is completed, the mixer blade, mixer can, proportionating machine and dosing system must all be cleaned for the next run. Approximately 10% of the batch is lost in the cleaning process.
The above-mentioned systems generally include an injection nozzle. As material is pumped through the injection nozzle, a volume of material is formed within the nozzle which over time passes through the nozzle and exits to fill containers.
Nozzles have been developed in the urethane foam dispensing arts which utilize a mixing shaft operatively disposed within the nozzle for producing mixing during an injection process. These shafts can include projections extending radially outwardly therefrom, appearing to be disposed in a cross-wise fashion extending from the center shaft when viewed in cross-section. Examples of such machines are low pressure two-component foam processing machines and nozzles manufactured by Edge-Sweets of Grand Rapids. Mich. Widen adapting such mixing nozzles to pigmenting sealants, the high viscosity of the sealant as well as the high viscosity of the pigments create mixing problems.
As stated above, the injected base material passes through the nozzles as a predetermined volume in the form of a column. The volume of material is initially a highly viscous heterogeneous mixture of materials. What is required is the mixing of the pigment, which is also highly viscous, into a homogeneous mixture with the highly viscous volume of sealant. It has been found that using the aforementioned nozzles having mixing shafts therein results in inadequate mixing of the highly viscous fluids. This is caused by adhesion of the highly viscous sealant to the mixing shaft as it passes therethrough as the cross-wise pins extending therefrom can define undisturbed columns of material which can travel along the shaft without being folded into the pigment and vice versa. Further, such machines, if sped up, produce shearing which increases temperature of the material. Increased temperatures are to be avoided as the increased temperatures can cause curing and other chemical modifications to the material. Such shearing is a dispersive type of mixing, similar to a grinding effect. With highly viscous materials, a folding-type mixing which is distributive, is desired which maintains a low temperature of the materials while thoroughly mixing the two materials together.
A further consideration of the present invention is that a small amount of pigment, less than 10% by weight of the total weight of the material, is required to be mixed in homogeneously throughout the length of the volume of sealant being ejected from the nozzle. Hence, folding which may begin at one end of the nozzle must be completed to homogeneity before it is injected from the other end of the nozzle and this must be done consistently throughout the length of the volume of material being ejected.
The present invention provides a dynamic mixing process which is designed to minimize clean-up and maximize the speed in changing from color to color while the entire mixing process is performed within the nozzle assembly of the present invention.